Interpretive Summary: Estimating densities of flying insects in agricultural crops should be useful in predicting future economic losses due to feeding damage. Insects are expected to fly at an average height with a vertical flight distribution that approximates a normal curve having a characteristic standard deviation (SD). Many studies in the literature report catches on blank (non-attractive) traps at several heights attached to poles. These catches were used to calculate an average flight height and SD that was then used to determine an effective flight layer, FL, for each insect species. An equation to estimate densities of flying insects per hectare (100 x 100 m) is presented that uses the FL, trapping time, the trap’s spherical effective radius (ER), catch at the mean flight height as estimated from a best fitting normal distribution with SD, and an estimated average flight speed over the ground. The calculated densities are undoubtedly imprecise since trapping times and average flight speeds were not well known. The same equation can use the effective attraction radius, EAR, for traps with pheromone lures or attractive colors. In practice, EAR is more useful than ER for flight density calculations since attractive traps would catch higher numbers of insects and can thus measure populations at lower amounts more easily. Computer simulations in three dimensions with varying numbers of insects per area (density) and varying EAR were used to validate the equations and indicate the reliability of the density estimates from field studies. Relatively few studies have provided data on insect catches that can be used to obtain EAR and FL in order to use these parameters to estimate flight densities per hectare, however, the necessary data can be obtained in future work.

Technical Abstract:
Insect species often exhibit a specific mean flight height and vertical flight distribution that approximates a normal distribution with a characteristic standard deviation (SD). Many studies in the literature report catches on passive (non-attractive) traps at several heights. These catches were used to calculate a mean flight height and SD that further can determine an effective flight layer, FL, for each insect species. An equation to estimate densities of flying insects per hectare is presented that uses the FL, trapping time, the trap’s spherical effective radius (ER), catch at the mean flight height as estimated from a best fitting normal distribution with SD, and an estimated average flight speed. The calculated densities are undoubtedly imprecise since trapping times and average flight speeds were poorly known in most reports. The same equation can use the effective attraction radius, EAR, for traps with semiochemical lures or attractive colors. In practice, EAR is more useful than ER for flight density calculations since attractive traps would catch higher numbers of insects and can thus measure lower populations more readily. Computer simulations in three dimensions with varying numbers of insects (density) and varying EAR were used to validate the equations and indicate the reliability of density estimates from field studies. Few studies have provided catch data to obtain EAR, FL and other data to estimate flight densities per hectare. However, the necessary data can be obtained in future work to estimate densities for treatment decisions in integrated pest management.